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<h1 id="一、信号驱动"><a href="#一、信号驱动" class="headerlink" title="一、信号驱动"></a><font size=3>一、信号驱动</font></h1><p>信号驱动是一种异步通知，异步通知的核心就是信号 ，所有的信号都定义在 linux 内核源码的这个文件中：</p>
<figure class="highlight shell"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">arch/xtensa/include/uapi/asm/signal.h </span><br></pre></td></tr></table></figure>

<h2 id="1-应用层"><a href="#1-应用层" class="headerlink" title="1.应用层"></a><font size=3>1.应用层</font></h2><p>使用信号驱动的时候，我们需要在应用层完成三件事，一是信号注册，二是将设备的IO模式设置成信号驱动模式，三是完成信号处理函数。</p>
<h3 id="1-1-signal"><a href="#1-1-signal" class="headerlink" title="1.1 signal()"></a><font size=3>1.1 signal()</font></h3><p>在 linux 下可以使用 man signal 命令查看该函数的帮助手册，大概会有两种函数声明形式，但是其实是一样的，习惯上会使用形式一。</p>
<div class="tabs" id="tabname1"><ul class="nav-tabs"><li class="tab active"><a href="#tabname1-1">声明形式一</a></li><li class="tab"><a href="#tabname1-2">声明形式二</a></li></ul><div class="tab-content"><div class="tab-pane active" id="tabname1-1"><p>【说明】使用的命令为 man signal 或者 man 2 signal 查询到的系统调用的函数声明形式。</p>
<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">/* 需包含的头文件 */</span></span><br><span class="line"><span class="meta">#<span class="keyword">include</span> <span class="string">&lt;signal.h&gt;</span></span></span><br><span class="line"><span class="comment">/* 函数声明 */</span></span><br><span class="line"><span class="keyword">typedef</span> <span class="title function_">void</span> <span class="params">(*<span class="type">sighandler_t</span>)</span><span class="params">(<span class="type">int</span>)</span>;</span><br><span class="line"><span class="type">sighandler_t</span> <span class="title function_">signal</span><span class="params">(<span class="type">int</span> signum, <span class="type">sighandler_t</span> handler)</span>;</span><br></pre></td></tr></table></figure></div><div class="tab-pane" id="tabname1-2"><p>【说明】使用 man 3 signal 查询到的库函数中的函数声明形式。</p>
<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">/* 需包含的头文件 */</span></span><br><span class="line"><span class="meta">#<span class="keyword">include</span> <span class="string">&lt;signal.h&gt;</span></span></span><br><span class="line"><span class="comment">/* 函数声明 */</span></span><br><span class="line"><span class="type">void</span> (*signal(<span class="type">int</span> sig, <span class="type">void</span> (*func)(<span class="type">int</span>)))(<span class="type">int</span>);</span><br></pre></td></tr></table></figure></div></div></div>

<details class="folding-tag" blue><summary> 点击查看两种声明的关系 </summary>
              <div class='content'>
              <p>我们先来看声明形式二：</p><figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line"><span class="type">void</span> (*signal(<span class="type">int</span> sig, <span class="type">void</span> (*func)(<span class="type">int</span>)))(<span class="type">int</span>);</span><br></pre></td></tr></table></figure><p>我们先拆分一下：</p><figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">/* 注意一下函数指针的形式：&lt;数据类型&gt; (*&lt;函数指针名称&gt;) (&lt;参数说明列表&gt;);  */</span></span><br><span class="line"><span class="type">void</span> (  ) (<span class="type">int</span>)</span><br><span class="line">      |</span><br><span class="line">      *signal(<span class="type">int</span> sig,   )</span><br><span class="line">                       |</span><br><span class="line">                       <span class="type">void</span> (*func)(<span class="type">int</span>)</span><br><span class="line">                              </span><br></pre></td></tr></table></figure><ul><li>由于 () 的存在， *func 是一个指针变量，后边的括号和 int 说明这个指针变量可以指向一个带有 int 形参的函数，前边的 void 说明这个函数指针指向的函数返回值为 void 类型，总的来说就是 void (*func)(int) 定义了一个函数指针变量 func ，它可以指向一个带有一个 int 参数的返回值为 void 类型的函数。可以指向的函数形式如下：</li></ul><figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line"><span class="type">void</span> <span class="title function_">functionName</span><span class="params">(<span class="type">int</span> arg)</span>;</span><br></pre></td></tr></table></figure><ul><li>再往上一层看，这就到了 signal 了， * 的优先级是低于 () 的，所以 signal 先与后边的 (int sig, void (*func)(int)) 相结合，说说明 signal 是一个函数，并且带有两个参数，一个是 int 类型的变量，一个是 void (*func)(int) 类型的函数指针变量。</li><li>再看 signal 前边的 * 表示这是一个指针变量，也就是说这个 signal 函数的返回值是一个指针变量。</li><li>接着就是最后的 (int) ，这表示， signal 函数返回的指针变量可以指向一个带有 int 类型参数的函数。</li><li>最前边的 void 表示， signal 函数返回的指针变量可以指向一个带有 int 类型参数且没有返回值的函数。</li></ul><p>总的来说，定义了一个指针函数 signal ，指针函数的返回值是一个函数指针，可以指向一个带有 int 类型参数且无返回值的函数；</p><p>而 signal 含有两个参数，一个是普通的整型变量，另一个是函数指针类型，可以指向带有一个 int 类型且无返回值的函数。</p><p>经过分析，会发现， signal 的返回值和 signal 函数第二个参数的类型是一样的，他们都是函数指针吗，都可以指向一个带有一个 int 类型参数的没有返回值的函数。</p><p>前边我们使用 typedef 简化过这样的定义的，所以这里，我们可以这样也做一个简化：</p><figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">typedef</span> <span class="title function_">void</span> <span class="params">(*pfunc)</span><span class="params">(<span class="type">int</span>)</span></span><br></pre></td></tr></table></figure><p>这样，上边的函数就可以写为：</p><figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">pfunc <span class="title function_">signal</span><span class="params">(<span class="type">int</span> sig, pfunc)</span>;<span class="comment">/* 需要注意的是，声明只需要类型即可，不一定需要写出形参*/</span></span><br></pre></td></tr></table></figure><p>这样是不是就跟前边形式一很像了呢？我们把 pfunc 换成 sighandler_t 其实就得到了形式一的声明，这完全是可以的，毕竟指针变量名只要符合标识规则即可</p>
              </div>
            </details>

<p><strong>【函数说明】</strong>该函数可以修改进程对信号的处理方式，可将信号的处理方式设置为捕获信号、忽略信号以及系统默认操作。</p>
<p><strong>【函数参数】</strong></p>
<ul>
<li>signum ： int 类型，此参数指定需要进行设置的信号，可使用信号名（宏）或信号的数字编号，不过一般建议使用信号名。</li>
<li>handler ： sighandler_t 类型，是一个函数指针，指向信号对应的信号处理函数，当进程接收到信号后会自动执行该处理函数；也可以指向几个预定义函数。</li>
</ul>
<details class="folding-tag" blue><summary> 点击查看 handler 可指向的预定义函数 </summary>
              <div class='content'>
              <table>    <tr><td align="center" width=150px>SIG_DFL</td><td align="left">表示设置为系统默认操作</td></tr>    <tr><td align="center" width=150px>SIG_IGN</td><td align="left">表示设置为忽视信号</td></tr></table>
              </div>
            </details>

<p><strong>【返回值】</strong> sighandler_t 类型，是一个函数指针，成功情况下的返回值则是指向在此之前的信号处理函数；如果出错则返回 SIG_ERR ，并会设置 errno 。</p>
<p><strong>【使用格式】</strong>一般情况下基本使用格式如下：</p>
<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">/* 需要包含的头文件 */</span></span><br><span class="line"><span class="meta">#<span class="keyword">include</span> <span class="string">&lt;signal.h&gt;</span></span></span><br><span class="line"></span><br><span class="line"><span class="comment">/* 至少应该有的语句 */</span></span><br><span class="line"><span class="keyword">typedef</span> <span class="title function_">void</span> <span class="params">(*<span class="type">sighandler_t</span>)</span><span class="params">(<span class="type">int</span>)</span>;<span class="comment">/* 不需要使用sighandler_t定义变量时，好像不写也可以 */</span></span><br><span class="line"><span class="type">void</span> <span class="title function_">sigintHandle</span><span class="params">(<span class="type">int</span> sig)</span>;</span><br><span class="line"></span><br><span class="line"><span class="comment">/* 需要函数返回值 */</span></span><br><span class="line"><span class="type">sighandler_t</span> oldact;</span><br><span class="line">oldact = signal(SIGINT, sigintHandle);</span><br><span class="line"><span class="comment">/* 或者不需要函数返回值 */</span></span><br><span class="line">signal(SIGINT, sigintHandle);</span><br></pre></td></tr></table></figure>

<p><strong>【注意事项】</strong>信号处理函数声明一般如下：</p>
<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line"><span class="type">void</span> <span class="title function_">handler</span><span class="params">(<span class="type">int</span> sig)</span>;</span><br></pre></td></tr></table></figure>

<h3 id="1-2-使用实例"><a href="#1-2-使用实例" class="headerlink" title="1.2 使用实例"></a><font size=3>1.2 使用实例</font></h3><figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br></pre></td><td class="code"><pre><span class="line"><span class="type">int</span> fd = <span class="number">-1</span>; <span class="comment">/* 文件描述符 */</span></span><br><span class="line"><span class="comment">/** 信号处理函数 */</span></span><br><span class="line"><span class="type">void</span> <span class="title function_">sigio_handler</span><span class="params">(<span class="type">int</span> signo)</span></span><br><span class="line">&#123;</span><br><span class="line">	<span class="comment">// 读写数据</span></span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line"><span class="type">int</span> <span class="title function_">main</span><span class="params">(<span class="type">int</span> argc, <span class="type">char</span> *argv[])</span></span><br><span class="line">&#123;</span><br><span class="line">	<span class="type">int</span> flag = <span class="number">0</span>;</span><br><span class="line">	<span class="comment">/* 1.判断参数个数是否合法 */</span></span><br><span class="line">	<span class="keyword">if</span> (argc &lt; <span class="number">2</span>)</span><br><span class="line">	&#123;</span><br><span class="line">		<span class="built_in">printf</span>(<span class="string">&quot;\n%s /dev/dev_name\n\n&quot;</span>, argv[<span class="number">0</span>]);</span><br><span class="line">		<span class="keyword">return</span> <span class="number">-1</span>;</span><br><span class="line">	&#125;</span><br><span class="line">	<span class="comment">/* 2.打开字符设备 */</span></span><br><span class="line">	<span class="keyword">if</span> ((fd = open(argv[<span class="number">1</span>], O_RDWR)) &lt; <span class="number">0</span>) <span class="comment">/* 默认就是阻塞的 */</span></span><br><span class="line">	&#123;</span><br><span class="line">		<span class="built_in">printf</span>(<span class="string">&quot;open %s failed\n&quot;</span>, argv[<span class="number">1</span>]);</span><br><span class="line">		<span class="keyword">return</span> <span class="number">-1</span>;</span><br><span class="line">	&#125;</span><br><span class="line">	<span class="comment">/* 3.注册信号处理函数 */</span></span><br><span class="line">	signal(SIGIO, sigio_handler);</span><br><span class="line">	<span class="comment">/* 4.开启异步通知相关操作 */</span></span><br><span class="line">	fcntl(fd, F_SETOWN, getpid()); <span class="comment">/* 将本应用程序的进程号告诉给内核 */</span></span><br><span class="line">	flag = fcntl(fd, F_GETFL);     <span class="comment">/* 获取当前的进程状态 */</span></span><br><span class="line">	flag |= FASYNC;</span><br><span class="line">	fcntl(fd, F_SETFL, flag);      <span class="comment">/* 开启当前进程异步通知功能 */</span></span><br><span class="line">	<span class="comment">/* 5.循环等待 */</span></span><br><span class="line">	<span class="keyword">while</span> (<span class="number">1</span>)</span><br><span class="line">	&#123;</span><br><span class="line">		sleep(<span class="number">1</span>);</span><br><span class="line">	&#125;</span><br><span class="line">	<span class="comment">/* 6.关闭字符设备 */</span></span><br><span class="line">	close(fd);</span><br><span class="line">	fd = <span class="number">-1</span>;</span><br><span class="line"></span><br><span class="line">	<span class="keyword">return</span> <span class="number">0</span>;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<h2 id="2-驱动层"><a href="#2-驱动层" class="headerlink" title="2.驱动层"></a><font size=3>2.驱动层</font></h2><h3 id="2-1-相关结构体"><a href="#2-1-相关结构体" class="headerlink" title="2.1 相关结构体"></a><font size=3>2.1 相关结构体</font></h3><h4 id="2-1-1-fasync-struct"><a href="#2-1-1-fasync-struct" class="headerlink" title="2.1.1 fasync_struct   "></a><font size=3>2.1.1 fasync_struct   </font></h4><p>在驱动中实现信号驱动前，我们需要在驱动程序中定义一个 fasync_struct 结构体指针变量，该结构体定义在 linux 内核源码的这个文件中：</p>
<figure class="highlight shell"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">include/linux/fs.h</span><br></pre></td></tr></table></figure>

<p>我们打开文件，该结构体定义如下：</p>
<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br></pre></td><td class="code"><pre><span class="line"><span class="class"><span class="keyword">struct</span> <span class="title">fasync_struct</span> &#123;</span></span><br><span class="line">        <span class="type">spinlock_t</span>              fa_lock;</span><br><span class="line">        <span class="type">int</span>                     magic;</span><br><span class="line">        <span class="type">int</span>                     fa_fd;</span><br><span class="line">        <span class="class"><span class="keyword">struct</span> <span class="title">fasync_struct</span>    *<span class="title">fa_next</span>;</span> <span class="comment">/* singly linked list */</span></span><br><span class="line">        <span class="class"><span class="keyword">struct</span> <span class="title">file</span>             *<span class="title">fa_file</span>;</span></span><br><span class="line">        <span class="class"><span class="keyword">struct</span> <span class="title">rcu_head</span>         <span class="title">fa_rcu</span>;</span></span><br><span class="line">&#125;;</span><br></pre></td></tr></table></figure>

<h3 id="2-2-相关函数"><a href="#2-2-相关函数" class="headerlink" title="2.2 相关函数"></a><font size=3>2.2 相关函数</font></h3><h4 id="2-2-1-fasync-helper"><a href="#2-2-1-fasync-helper" class="headerlink" title="2.2.1 fasync_helper  ()"></a><font size=3>2.2.1 fasync_helper  ()</font></h4><p>我们使用以下命令查询一下函数所在头文件：</p>
<figure class="highlight shell"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">grep fasync_helper -r -n ~/5linux/linux-3.14/include</span><br></pre></td></tr></table></figure>

<p>经过查找，我们可以得到如下信息：</p>
<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">/* 需包含的头文件 */</span></span><br><span class="line"><span class="meta">#<span class="keyword">include</span> <span class="string">&lt;linux/fs.h&gt;</span></span></span><br><span class="line"></span><br><span class="line"><span class="comment">/* 函数声明 */</span></span><br><span class="line"><span class="keyword">extern</span> <span class="type">int</span> <span class="title function_">fasync_helper</span><span class="params">(<span class="type">int</span>, <span class="keyword">struct</span> file *, <span class="type">int</span>, <span class="keyword">struct</span> fasync_struct **)</span>;</span><br><span class="line"><span class="comment">/* 函数定义，定义在 fs/fcntl.c 文件 */</span></span><br><span class="line"><span class="comment">/*</span></span><br><span class="line"><span class="comment"> * fasync_helper() is used by almost all character device drivers</span></span><br><span class="line"><span class="comment"> * to set up the fasync queue, and for regular files by the file</span></span><br><span class="line"><span class="comment"> * lease code. It returns negative on error, 0 if it did no changes</span></span><br><span class="line"><span class="comment"> * and positive if it added/deleted the entry.</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"><span class="type">int</span> <span class="title function_">fasync_helper</span><span class="params">(<span class="type">int</span> fd, <span class="keyword">struct</span> file * filp, <span class="type">int</span> on, <span class="keyword">struct</span> fasync_struct **fapp)</span></span><br><span class="line">&#123;</span><br><span class="line">        <span class="keyword">if</span> (!on)</span><br><span class="line">                <span class="keyword">return</span> fasync_remove_entry(filp, fapp);</span><br><span class="line">        <span class="keyword">return</span> fasync_add_entry(fd, filp, fapp);</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<p><strong>【函数说明】</strong>该函数用于初始化或者释放定义的 fasync_struct 结构体指针 。</p>
<p><strong>【函数参数】</strong></p>
<ul>
<li>fd ：int 类型，表示要操作的文件描述符。</li>
<li>filp ： struct file *  类型， 读写文件内容过程中用到的一些控制性数据组合而成的对象。  </li>
<li>on ：int 类型，非0，表示初始化异步通知结构体指针，为0，表示释放异步通知结构体指针。</li>
<li>fapp ：struct fasync_struct ** 类型，要初始化的 fasync_struct 结构体指针变量。</li>
</ul>
<p><strong>【返回值】</strong>int 类型，成功返回非负数（&gt;&#x3D;0），失败返回一个负数  </p>
<p><strong>【使用格式】</strong></p>
<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">/* 需包含的头文件 */</span></span><br><span class="line"><span class="meta">#<span class="keyword">include</span> <span class="string">&lt;linux/fs.h&gt;</span></span></span><br><span class="line"></span><br><span class="line"><span class="comment">/* 至少要有的语句 */</span></span><br><span class="line"><span class="class"><span class="keyword">struct</span> <span class="title">fasync_struct</span> *<span class="title">pasync_obj</span>;</span></span><br><span class="line"><span class="comment">// 释放pasync_obj</span></span><br><span class="line">fasync_helper(<span class="number">-1</span>, pfile, <span class="number">0</span>, &amp;pasync_obj); <span class="comment">// 释放pasync_obj</span></span><br><span class="line"><span class="comment">// 初始化pasync_obj</span></span><br><span class="line"><span class="type">static</span> <span class="type">int</span> <span class="title function_">mydev_fasync</span><span class="params">(<span class="type">int</span> fd, <span class="keyword">struct</span> file *pfile, <span class="type">int</span> mode)</span></span><br><span class="line">&#123;</span><br><span class="line">    <span class="class"><span class="keyword">struct</span> _<span class="title">my_dev</span> *<span class="title">p_my_dev</span> =</span> (<span class="keyword">struct</span> _my_dev *)(pfile-&gt;private_data); <span class="comment">/* 通过私有数据方式获取 g_my_dev设备属性 */</span></span><br><span class="line">    <span class="keyword">return</span> (fasync_helper(fd, pfile, mode, &amp;p_my_dev-&gt;pasync_obj));</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<p><strong>【注意事项】</strong> 当应用程序通过下边的语句改变 fasync 标记的时候，驱动程序 file_operations 操作集中我们自己实现的 fasync 函数就会执行。  </p>
<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">fcntl(fd, F_SETFL, flags | FASYNC);</span><br></pre></td></tr></table></figure>

<h4 id="2-2-2-kill-fasync"><a href="#2-2-2-kill-fasync" class="headerlink" title="2.2.2 kill_fasync ()"></a><font size=3>2.2.2 kill_fasync ()</font></h4><p>我们使用以下命令查询一下函数所在头文件：</p>
<figure class="highlight shell"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">grep kill_fasync -r -n ~/5linux/linux-3.14/include</span><br></pre></td></tr></table></figure>

<p>经过查找，我们可以得到如下信息：</p>
<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">/* 需包含的头文件 */</span></span><br><span class="line"><span class="meta">#<span class="keyword">include</span> <span class="string">&lt;linux/fs.h&gt;</span></span></span><br><span class="line"></span><br><span class="line"><span class="comment">/* 函数声明 */</span></span><br><span class="line"><span class="keyword">extern</span> <span class="type">void</span> <span class="title function_">kill_fasync</span><span class="params">(<span class="keyword">struct</span> fasync_struct **, <span class="type">int</span>, <span class="type">int</span>)</span>;</span><br><span class="line"><span class="comment">/* 函数定义，定义在 fs/fcntl.c 文件 */</span></span><br><span class="line"><span class="type">void</span> <span class="title function_">kill_fasync</span><span class="params">(<span class="keyword">struct</span> fasync_struct **fp, <span class="type">int</span> sig, <span class="type">int</span> band)</span></span><br><span class="line">&#123;</span><br><span class="line">        <span class="comment">/* First a quick test without locking: usually</span></span><br><span class="line"><span class="comment">         * the list is empty.</span></span><br><span class="line"><span class="comment">         */</span></span><br><span class="line">        <span class="keyword">if</span> (*fp) &#123;</span><br><span class="line">                rcu_read_lock();</span><br><span class="line">                kill_fasync_rcu(rcu_dereference(*fp), sig, band);</span><br><span class="line">                rcu_read_unlock();</span><br><span class="line">        &#125;</span><br><span class="line">&#125;</span><br><span class="line"></span><br></pre></td></tr></table></figure>

<p><strong>【函数说明】</strong>当设备可以访问的时候，驱动程序需要向应用程序发出信号，相当于产生“中断”。 kill_fasync() 函数负责发送指定的信号   。</p>
<p><strong>【函数参数】</strong></p>
<ul>
<li>fp ：struct fasync_struct ** 类型，要操作的 fasync_struct 类型指针变量。</li>
<li>sig ： int  类型， 要发送的信号，一般是SIGIO。  </li>
<li>band ：int 类型，可读时设置为 POLL_IN，可写时设置为 POLL_OUT。</li>
</ul>
<p><strong>【返回值】</strong>none</p>
<p><strong>【使用格式】</strong></p>
<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">/* 需包含的头文件 */</span></span><br><span class="line"><span class="meta">#<span class="keyword">include</span> <span class="string">&lt;linux/fs.h&gt;</span></span></span><br><span class="line"></span><br><span class="line"><span class="comment">/* 至少要有的语句 */</span></span><br><span class="line"><span class="class"><span class="keyword">struct</span> <span class="title">fasync_struct</span> *<span class="title">pasync_obj</span>;</span></span><br><span class="line">kill_fasync(&amp;pasync_obj, SIGIO, POLL_IN);</span><br></pre></td></tr></table></figure>

<p><strong>【注意事项】</strong> none</p>
<h3 id="2-3-使用实例"><a href="#2-3-使用实例" class="headerlink" title="2.3 使用实例"></a><font size=3>2.3 使用实例</font></h3><h4 id="2-3-1-初始化异步通知结构体"><a href="#2-3-1-初始化异步通知结构体" class="headerlink" title="2.3.1 初始化异步通知结构体"></a><font size=3>2.3.1 初始化异步通知结构体</font></h4><figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">/**</span></span><br><span class="line"><span class="comment"> * @Function    : mydev_fasync</span></span><br><span class="line"><span class="comment"> * @brief       : 应用调用fcntl设置FASYNC时调用该函数产生异步通知结构对象，并将其地址设置到设备结构成员中</span></span><br><span class="line"><span class="comment"> * @param fd    ：int 类型，文件描述符。</span></span><br><span class="line"><span class="comment"> * @param pfile : struct file *  类型，指向open产生的struct file类型的对象，表示本次ioctl对应的那次open。</span></span><br><span class="line"><span class="comment"> *                                    (读写文件内容过程中用到的一些控制性数据组合而成的对象)</span></span><br><span class="line"><span class="comment"> * @param mode  ：int 类型，。</span></span><br><span class="line"><span class="comment"> * @return      : 异步通知结构对象</span></span><br><span class="line"><span class="comment"> * @Description : 函数名初始化给struct file_operations的成员.fasync</span></span><br><span class="line"><span class="comment"> *                结构体指针变量。当应用程序通过 “ fcntl(fd, F_SETFL, flags | FASYNC)” 改变</span></span><br><span class="line"><span class="comment"> *                fasync标记的时候，驱动程序 file_operations操作集中的 fasync函数就会执行。</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"><span class="type">static</span> <span class="type">int</span> <span class="title function_">mydev_fasync</span><span class="params">(<span class="type">int</span> fd, <span class="keyword">struct</span> file *pfile, <span class="type">int</span> mode)</span></span><br><span class="line">&#123;</span><br><span class="line">    <span class="class"><span class="keyword">struct</span> _<span class="title">my_dev</span> *<span class="title">p_my_dev</span> =</span> (<span class="keyword">struct</span> _my_dev *)(pfile-&gt;private_data); <span class="comment">/* 通过私有数据方式获取 g_my_dev设备属性 */</span></span><br><span class="line">    <span class="comment">/* 创建异步通知结构对象 */</span></span><br><span class="line">    <span class="keyword">return</span> (fasync_helper(fd, pfile, mode, &amp;p_my_dev-&gt;pasync_obj));</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<h4 id="2-3-2-释放异步通知结构体变量"><a href="#2-3-2-释放异步通知结构体变量" class="headerlink" title="2.3.2 释放异步通知结构体变量"></a><font size=3>2.3.2 释放异步通知结构体变量</font></h4><figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">/**</span></span><br><span class="line"><span class="comment"> * @Function    : mydev_close</span></span><br><span class="line"><span class="comment"> * @brief       : 关闭设备</span></span><br><span class="line"><span class="comment"> * @param pnode : struct inode * 类型，内核中记录文件元信息的结构体</span></span><br><span class="line"><span class="comment"> * @param pfile : struct file *  类型，读写文件内容过程中用到的一些控制性数据组合而成的对象</span></span><br><span class="line"><span class="comment"> * @return      : 0,操作完成</span></span><br><span class="line"><span class="comment"> * @Description : 函数名初始化给 struct file_operations 的成员 .close</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"><span class="type">int</span> <span class="title function_">mydev_close</span><span class="params">(<span class="keyword">struct</span> inode *pnode, <span class="keyword">struct</span> file *pfile)</span></span><br><span class="line">&#123;</span><br><span class="line">    <span class="class"><span class="keyword">struct</span> _<span class="title">my_dev</span> *<span class="title">p_my_dev</span> =</span> (<span class="keyword">struct</span> _my_dev *)(pfile-&gt;private_data); <span class="comment">/* 通过私有数据方式获取 g_my_dev设备属性 */</span></span><br><span class="line">    <span class="comment">/* 释放异步通知结构对象 */</span></span><br><span class="line">    <span class="keyword">if</span> (p_my_dev-&gt;pasync_obj != <span class="literal">NULL</span>)</span><br><span class="line">        fasync_helper(<span class="number">-1</span>, pfile, <span class="number">0</span>, &amp;p_my_dev-&gt;pasync_obj);</span><br><span class="line">    printk(<span class="string">&quot;mydev_close is called!\n&quot;</span>);</span><br><span class="line">    <span class="keyword">return</span> <span class="number">0</span>;</span><br><span class="line">&#125;</span><br><span class="line"></span><br></pre></td></tr></table></figure>

<h4 id="2-3-4-发送信号"><a href="#2-3-4-发送信号" class="headerlink" title="2.3.4 发送信号"></a><font size=3>2.3.4 发送信号</font></h4><figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">/**</span></span><br><span class="line"><span class="comment"> * @Function    : mydev_write</span></span><br><span class="line"><span class="comment"> * @brief       : 写设备</span></span><br><span class="line"><span class="comment"> * @param pfile : struct file *  类型，指向open产生的struct file类型的对象，表示本次write对应的那次open。</span></span><br><span class="line"><span class="comment"> *                                    (读写文件内容过程中用到的一些控制性数据组合而成的对象)</span></span><br><span class="line"><span class="comment"> * @param pbuf  ：__user * 类型，指向用户空间一块内存，用来保存被写的数据。</span></span><br><span class="line"><span class="comment"> * @param count ：size_t   类型，用户期望写入的字节数。</span></span><br><span class="line"><span class="comment"> * @param ppos  ：loff_t * 类型，对于需要位置指示器控制的设备操作有用，用来指示写入的起始位置，写完后也需要变更位置指示器的指示位置。</span></span><br><span class="line"><span class="comment"> * @return      : 成功返回本次成功写入的字节数，失败返回-1</span></span><br><span class="line"><span class="comment"> * @Description : 函数名初始化给 struct file_operations 的成员 .write</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"><span class="type">ssize_t</span> <span class="title function_">mydev_write</span><span class="params">(<span class="keyword">struct</span> file *pfile, <span class="type">const</span> <span class="type">char</span> __user *pbuf, <span class="type">size_t</span> count, <span class="type">loff_t</span> *ppos)</span></span><br><span class="line">&#123;</span><br><span class="line">    <span class="comment">// 其他操作... ...</span></span><br><span class="line">    <span class="comment">/* 写函数中有数据可读时向应用层发信号 */</span></span><br><span class="line">    <span class="comment">/** kill_fasync:发信号</span></span><br><span class="line"><span class="comment">     *              struct fasync_struct ** 指向保存异步通知结构地址的指针</span></span><br><span class="line"><span class="comment">     *              int 	信号 SIGIO/SIGKILL/SIGCHLD/SIGCONT/SIGSTOP</span></span><br><span class="line"><span class="comment">     *              int 	读写信息POLLIN、POLLOUT </span></span><br><span class="line"><span class="comment">     */</span></span><br><span class="line">    <span class="keyword">if</span> (p_my_dev-&gt;pasync_obj != <span class="literal">NULL</span>)</span><br><span class="line">        kill_fasync(&amp;p_my_dev-&gt;pasync_obj, SIGIO, POLL_IN);</span><br><span class="line">    <span class="keyword">return</span> size;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<h2 id="3-使用步骤"><a href="#3-使用步骤" class="headerlink" title="3. 使用步骤"></a><font size=3>3. 使用步骤</font></h2><h3 id="3-1-应用层"><a href="#3-1-应用层" class="headerlink" title="3.1 应用层"></a><font size=3>3.1 应用层</font></h3><ul>
<li>（1）注册信号处理函数</li>
</ul>
<p>应用程序根据驱动程序所使用的信号来设置信号的处理函数，应用程序使用 signal 函数来设置信号的处理函数。</p>
<ul>
<li>（2）将本应用程序的进程号告诉给内核</li>
</ul>
<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">fcntl(fd, F_SETOWN, getpid());</span><br></pre></td></tr></table></figure>

<ul>
<li>（3）开启异步通知</li>
</ul>
<figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line">flags = fcntl(fd, F_GETFL); <span class="comment">/* 获取当前的进程状态 */</span></span><br><span class="line">fcntl(fd, F_SETFL, flags | FASYNC); <span class="comment">/* 开启当前进程异步通知功能 */</span></span><br></pre></td></tr></table></figure>

<p>经过这一步，驱动程序中的 fasync 函数就会执行。  </p>
<h3 id="3-2-驱动层"><a href="#3-2-驱动层" class="headerlink" title="3.2 驱动层"></a><font size=3>3.2 驱动层</font></h3><ul>
<li>（1）定义struct fasync_struct类型结构体指针变量；</li>
<li>（2）初始化struct fasync_struct结构体指针变量；</li>
<li>（3）发送信号；</li>
<li>（4）关闭设备时释放struct fasync_struct结构体指针变量。</li>
</ul>

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